The present invention relates to mesoporous silicate-coated nanoparticles, hollow mesoporous silicate nano-shells, and colloidal synthesis methods for producing the nanoparticles and nano-shells. More particularly, this method allows for depositing a controlled-porosity silicate shell around nanoparticles.
Mesoporous materials possess pore structure with diameters in the nanometer range. Chemically passive, electrically insulating, and optically transparent, silica nanocomposites of sub-micron particle size have applications, for example, as low dielectric constant insulators in nano-capacitors and semiconductor devices. Controlled porosity nanocomposites may find applications, for example, in the areas of chromatography, photographic imaging, and pigmentation, as well as in drug delivery. Mesoporous silicate-coated nanoparticles and nano-shells for use in other applications are within the scope of this invention.
The first nanocomposites of sub-micron length scale containing mesoporous silica and gold nanoparticles ranging in size from 1 to 3 nm were prepared using an aerosol-assisted self-assembly method. “Aerosol-assisted self-assembly of mesostructured spherical nanoparticles,” Yunfeng Lu, Hongyou Fan, Aaron Stump, Timothy L. Ward, Thomas Rieker and C. Jeffrey Brinker, Nature, 1999, 398, 223-226. Inverse micelles were used to stabilize gold nanoparticles, and to deliver them into the hydrophobic mesopores of the silicate material as it self-assembled, and the resulting nano-meter sized composite contained multiple gold particles.
In another method, microporous (Angstrom-sized pores) silicate nano-shells have been developed as inert protective shells around semiconductor and metal nanoparticles whose optical properties are intimately tied to the particle size and the surface conditions. See, e.g., “Synthesis of Nanosized Gold-Silica Core-Shell Particles,” Luis M. Liz-Marzan, Michael Giersig, and Paul Mulvaney, Langmuir, 1996, 12, 4329-4335. By covering metal nanoparticles with a thin layer of transparent silicate, the optical properties of these nanoparticles are preserved. This prior art method involved slow polymerization of sodium silicate or tetramethyl-sodium silicate under basic conditions. Chemical dissolution of the metal nanoparticle core resulted in the formation of hollow silicate shells with central diameters defined by the size of the original nanoparticle.
The present invention is directed to silicate nanoparticles and nano-shells with tailored porosity. The methods of the present invention provide systematic control of the thickness, porosity, and pore structure of a nanometers-thick mesoporous silicate coating. For example, mono-disperse spherical nanocomposites approximately 400±100 nm in diameter of mesoporous silicate and a single gold particle approximately 60 nm in diameter have been prepared using exemplary liquid-phase self-assembly processes of the present invention. In other embodiments, spherical mesoporous nanoparticles from 65 to 740 nm have been achieved. Thickness, porosity, and pore structure may be controlled to produce nanoparticles and nano-shells tailored to a specific application. For example, controlled porosity silicate coatings may be used to protect and control the chemical reactions of active particles encapsulated within. Among other things, controlled porosity nano-shells can be used to create specialized chemical nano-environments for reactive molecules. Some of the species that can be encapsulated in these particles include metal nanoparticles, metal oxide nanoparticles, nanocatalysts, organic dye molecules, flavors and aromas, and biochemicals such as DNA, RNA, proteins, and enzymes. Moreover, controlled porosity allows use in conditions that are chemically harsh, poisoning, or denaturing.
Another aspect of the invention is the controlled delivery of an active species trapped inside a controlled porosity silicate nanoshells, allowing control of macroscale reaction and release/diffusion rates. The porous network can be chemically modified in a post-processing step and can yield particles that are chemically selective, by slowing or enhancing the diffusion of one type of molecule or ion over others. The ability to create chemically tailored and chemically active units with chemistry controlled by the nature of the shell has the potential to revolutionize the field of chemical and biochemical catalysis. For example, mixing and matching of these species allows the design of complex reactor membranes for sequential chemical and biochemical reactions.
The chemically passive, electrically insulating, and optically transparent silica nanocomposites of sub-micron particle size of this invention are useful low dielectric constant insulators in nano-capacitors and semiconductor devices. In addition, the controlled nanometers-thick mesoporous silicate coating of the present invention are useful in the areas of chromatography, photographic imaging, and pigmentation, as well as in drug delivery.
An additional aspect of the present method is the use of nano-shells to control the delivery of the nano-shell contents over a long period of time, for example, to create reliable implantable patches for slow-release of drugs and medicines such as insulin. This is a particularly well-suited application, as silicate is biologically and chemically inert. Therefore, silicate patches with designed delivery characteristics may maintain their programmed release rates over extended periods in contrast to existing technologies, in which biodegradable polymer coatings change their release patterns as a function of time.
Another aspect of the present method is that controlled porosity silicate nanoshells may be used to create a high-density, high surface capacity powder. The controlled porosity of the silicate nanoshells may be exploited for the storage of volatile gaseous species such as hydrogen, oxygen, or methane. The nanoshells also may be used in the design of novel fuel cells and other energy storage devices that could be used in objects such as automobiles, airplanes, and rockets.
Additional features of the present method will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the method as presently perceived.